Southern Ocean

Repeated measurements of depth pro"les of Th (dissolved, 1}70 and '70 m particulate) at three stations (Orca, Minke, Sei) in the Ross Sea have been used to estimate the export of Th and particulate organic carbon (POC) from the euphotic zone. Sampling was carried out on three JGOFS cruises covering the period from October 1996 (austral early spring) to April 1997 (austral fall). De"ciencies of Th relative to its parent U in the upper 100 m are small during the early spring cruise, increase to maximum values during the summer, and decrease over the course of the fall. Application of a non-steady-state model to the Th data shows that the #ux of Th from the euphotic zone occurs principally during the summer cruise and in the interval between summer and fall. Station Minke in the southwestern Ross Sea appears to sustain signi"cant Th removal for a longer period than is evident at Orca or Sei. Particulate Th activities and POC are greater in the 1}70 m size fraction, except late in the summer cruise, when the '70 m POC fraction exceeds that of the 1}70 m fraction. The POC/Th ratio in the '70 m fraction exceeds that in the 1}70 m fraction, likely due in part to the greater availability of surface sites for Th adsorption in the latter. Particulate Th #uxes are converted to POC #uxes by multiplying by the POC/Th ratio of the '70 m fraction (assumed to be representative of sinking particles). POC #uxes calculated from a steady-state Th scavenging model range from 7 to 91 mmol C m\ d\ during late January}early February, with the greatest #ux observed at station Minke late in the cruise. Fluxes estimated with a non-steady-state Th model are 85 mmol C m\ d\ at Minke

Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It is associated with (1) colder and fresher surfacewater conditions in the North Atlantic, Labrador and Norwegian Seas, and (2) a weaker ventilation of North Atlantic deep waters during the early LIG (129-125 ka) compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka) than the late LIG (122 ka). Hence, insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. Additionally, we consider an idealized meltwater scenario at 126 ka where the freshwater input is interactively computed in response to the high boreal summer insolation. The model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka) compared to the late LIG (122 ka). This result suggests that both insolation and ice sheet melting have to be considered to reproduce the climatic pattern that we identify during the early LIG. Our modeldata comparison also reveals a number of limitations and reinforces the need for further detailed investigations using coupled climate-ice sheet models and transient simulations.

This paper is the first part of a twofold contribution dedicated to the new version of the Louvain-la-Neuve sea ice model LIM3. In this part, LIM3 is described and its results are compared with observations. LIM3 is a C-grid dynamic-thermodynamic model, including the representation of the subgrid-scale distributions of ice thickness, enthalpy, salinity and age. Brine entrapment and drainage as well as brine impact on ice thermodynamics are explicitly included. LIM3 is embedded into the ocean modelling system NEMO, using OPA9, a hydrostatic, primitive equation, finite difference ocean model in the 2°Â 2°cos/ configuration ORCA2. Model performance is evaluated by performing a hindcast of the Arctic and Antarctic sea ice packs, forced by a combination of daily NCEP/NCAR reanalysis data and various climatologies. The annual cycle of sea ice growth and decay is very realistically captured with ice area, thickness, drift and snow depth in good agreement with observations. In the Arctic, the simulated geographical distributions of ice thickness and concentration are significantly improved when compared with earlier versions of LIM. Model deficiencies feature an overestimation (underestimation) of ice thickness in the Beaufort gyre (around the North Pole) as well as an underestimation of ice thickness in the Southern Ocean. The simulated first year/multiyear sea ice limit agrees with observations. The values and distribution of sea ice age in the perennial ice zone are different from satellite-derived values, which is attributed to the different definitions of ice age. In conclusion, in light of the exhaustive sea ice analysis presented here, LIM3 is found to be an appropriate tool for large-scale sea ice and climate simulations.

Seagrasses, marine flowering plants, are widely distributed along temperate and tropical coastlines of the world. Seagrasses have key ecological roles in coastal ecosystems and can form extensive meadows supporting high biodiversity. The global species diversity of seagrasses is low (< 60 species), but species can have ranges that extend for thousands of kilometers of coastline. Seagrass bioregions are defined here, based on species assemblages, species distributional ranges, and tropical and temperate influences. Six global bioregions are presented: four temperate and two tropical. The temperate bioregions include the Temperate North Atlantic, the Temperate North Pacific, the Mediterranean, and the Temperate Southern Oceans. The Temperate North Atlantic has low seagrass diversity, the major species being Zostera marina, typically occurring in estuaries and lagoons. The Temperate North Pacific has high seagrass diversity with Zostera spp. in estuaries and lagoons as well as Phyllospadix spp. in the surf zone. The Mediterranean region has clear water with vast meadows of moderate diversity of both temperate and tropical seagrasses, dominated by deep-growing Posidonia oceanica. The Temperate Southern Oceans bioregion includes the temperate southern coastlines of Australia, Africa and South America. Extensive meadows of low-to-high diversity temperate seagrasses are found in this bioregion, dominated by various species of Posidonia and Zostera. The tropical bioregions are the Tropical Atlantic and the Tropical Indo-Pacific, both supporting mega-herbivore grazers, including sea turtles and sirenia. The Tropical Atlantic bioregion has clear water with a high diversity of seagrasses on reefs and shallow banks, dominated by Thalassia testudinum. The vast Tropical Indo-Pacific has the highest seagrass diversity in the world, with as many as 14 species growing together on reef flats although seagrasses also occur in very deep waters. The global distribution of seagrass genera is remarkably consistent north and south of the equator; the northern and southern hemispheres share ten seagrass genera and only have one unique genus each. Some genera are much more speciose than others, with the genus Halophila having the most seagrass species. There are roughly the same number of temperate and tropical seagrass genera as well as species. The most widely distributed seagrass is Ruppia maritima, which occurs in tropical and temperate zones in a wide variety of habitats. Seagrass bioregions at the scale of ocean basins are identified based on species distributions which are supported by genetic patterns of diversity. Seagrass bioregions provide a useful framework for interpreting ecological, physiological and genetic results collected in specific locations or from particular species.

Downward solar irradiance at the sea surface, measured on several voyages of an icebreaker in the Southern Ocean, is used to infer transmittance of solar radiation by clouds. Together with surface albedo estimated from coincident hourly sea ice reports, instantaneous cloud radiative forcing and effective cloud optical depth are obtained. Values of “raw cloud transmittance” (trc), the ratio of downward irradiance under cloud to downward irradiance measured under clear sky, vary from 0.1 to 1.0. Over sea ice, few values of trc were observed between 0.8 and 1.0, possibly due to the threshold nature of the aerosol-to-cloud-droplet transition. This sparsely populated region of transmittances is referred to as the Köhler gap.The instantaneous downward shortwave cloud radiative forcing is computed, as well as the time-averaged net forcing. The net forcing at a solar zenith angle of 60° is typically -250 W m-2 over open ocean, but only half this value over sea ice because of the higher surface albedo and less frequent occurrence of clouds.“Effective” optical depths τ (for a radiatively equivalent horizontally homogeneous cloud) are classified by season and surface type. The frequency distributions of τ are well fitted by decaying exponentials, giving a characteristic optical depth of 15 at 47°S, increasing to 24 in the region of maximum cloud cover at 58°S, and decreasing to 11 at 67°S near the coast of Antarctica.

The variability of Southern Ocean sea-surface temperatures (SST) are important to understanding coastal biology yet are poorly known amongst biologists. We compare sea temperatures at a constant depth (10-20 m) at coastal localities both sides of the Polar Front (PF), around the Scotia-Arc, the West Antarctic Peninsula and at high oceanic latitudes (around the margins of East Antarctica). We assess the wider context of these values by investigating minimum and maximum temperatures and ranges throughout the Southern Ocean using remotely sensed SST data. Data to date show weekly, daily and hourly variation in shallow sea temperature can be one-third of total annual variability (in the summer) but can be very constant (in winter). From comparison across scales in time and space, the strong seasonal signal is the most striking feature of Antarctic shallow sea temperatures even at highest oceanic latitude sites. The winter sea temperatures at localities within the PF are similar (near freezing), but upper temperatures and thus the annual range vary predictably with latitude in a cline. This amounts to 0.2 1C annual range/100 km of latitude between $541S and 671S. The annual range in sea temperatures is little different at SubAntarctic islands, whether they are north or south of the PF. r

a b s t r a c t Four grid surveys were carried out in the top 200 m layer of the Lazarev Sea during fall 2004, summer 2005-06, winter 2006 and summer 2007-08 onboard the R.V. Polarstern as a part of the German SO-GLOBEC. The distribution, abundance and biology of two species of salps, Salpa thompsoni and Ihlea racovitzai, were investigated. With the exception of fall 2004, I. racovitzai dominated the salp community although being represented by low densities (o 20 ind. 1000 m À 3 ). S. thompsoni was scarce during the summers of 2005-06 and 2007-08 and almost absent from the region during winter 2006. Nevertheless, it was modestly numerous during fall 2004 reaching densities of up to 33 ind. 1000 m À 3 in the southwestern stations of the grid. The data on the seasonal population structure and life cycle of I. racovitzai

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims were to examine the separate effects of each variable and to generate a predictive model of growth based on satellite-derivable environmental data. Both growth increments in length on moulting (GIs) and daily growth rates (DGRs, mm d Ϫ1 ) ranged greatly among the 59 swarms, from 0.58-15% and 0.013-0.32 mm d Ϫ1 . However, all swarms maintained positive mean growth, even those in the low chlorophyll a (Chl a) zone of the central Scotia Sea. Among a suite of indices of food quantity and quality, large-scale monthly Chl a values from SeaWiFS predicted krill growth the best. Across our study area, the great contrast between bloom and nonbloom regions was a major factor driving variation in growth rates, obscuring more subtle effects of food quality. GIs and DGRs decreased with increasing krill length and decreased above a temperature optimum of 0.5ЊC. This probably reflects the onset of thermal stress at the northern limit of krill's range. Thus, growth rates were fastest in the ice edge blooms of the southern Scotia Sea and not at South Georgia as previously suggested. This reflects both the smaller size of the krill and the colder water in the south being optimum for growth. Males tended to have higher GIs than females but longer intermoult periods, leading to similar DGRs between sexes. DGRs of equivalent-size krill tended to decrease with maturity stage, suggesting the progressive allocation of energy toward reproduction rather than somatic growth. Our maximum DGRs are higher than most literature values, equating to a 5.7% increase in mass per day. This value fits within a realistic energy budget, suggesting a maximum carbon ration of ϳ20% d Ϫ1 . Over the whole Scotia Sea/South Georgia area, the gross turnover of krill biomass was ϳ1% d Ϫ1 .

We attached satellite tags to 16 humpback whales off South Eastern Australia in October/November 2008. The tags transmitted for an average of 55 days (range: 3-156 days) and provided data on migratory movements between Australia and the Antarctic feeding grounds. While the dispersal into the Southern Ocean was generally consistent with movements determined from historical discovery marks, unexpected findings included an eastwards migration of eight whales to SW New Zealand, regular feeding in temperate latitudes (areas of high productivity) and a migration of one whale into Area IV. A full analysis of these data, with a focus on habitat utilization, will be developed.

A generalized coccolithophore bloom classifier has been developed for use with ocean color imagery. The bloom classifier was developed using extracted satellite reflectance data from SeaWiFS images screened by the default bloom detection mask. In the current application, we extend the optical water type (OWT) classification scheme by adding a new coccolithophore bloom class formed from these extracted reflectances. Based on an in situ coccolithophore data set from the North Atlantic, the detection levels with the new scheme were between 1,500 and 1,800 coccolithophore cells/mL and 43,000 and 78,000 liths/mL. The detected bloom area using the OWT method was an average of 1.75 times greater than the default bloom detector based on a collection of SeaWiFS 1 km imagery. The versatility of the scheme is shown with SeaWiFS, MODIS Aqua, CZCS and MERIS imagery at the 1 km scale. The OWT scheme was applied to the daily global SeaWiFS imagery mission data set (years 1997-2010). Based on our results, average annual coccolithophore bloom area was more than two times greater in the southern hemisphere compared to the northern hemisphere with values of 2.00 × 10 6 km 2 and 0.75 × 10 6 km 2 , respectively. The new algorithm detects larger bloom areas in the Southern Ocean compared to the default algorithm, and our revised global annual average of 2.75 × 10 6 km 2 is dominated by contributions from the Southern Ocean.

We investigated the composition, distribution and abundance of micro-and mesozooplankton in the Southern Ocean, south of Australia during the austral summer (DecembereFebruary) of the 2007/08 season using a Continuous Plankton Recorder (CPR). Four CPR tows were conducted during two separate oceanographic voyages under the CEAMARC (Collaborative East Antarctic Marine Census) project. High zooplankton abundance was recorded on each transect in the Polar Frontal Zone (PFZ) and the Inter Polar Frontal Zone (IPFZ). The community structure in these zones was dominated by common taxa including the ubiquitous small calanoid copepods, Oithona similis and Calanus simillimus, accounting for >70% of the total abundance, and copepod nauplii, foraminiferans and appendicularians of the genus Fritillaria spp. also occurred along most of the survey transects. Total zooplankton abundance was comparatively consistent along the four transects, and ranged between 119.8 and 144.7 ind m À3. The results of cluster and IndVal analyses revealed that the dominant species/taxa show similar associations, abundance and distribution patterns on all four transects. There was no evidence of a change of surface zooplankton abundance at the time of towing in this study. Detecting the various distribution patterns of micro-and mesozooplankton species/taxa, and the accumulation of high quality data collected by a consistent methodology will contribute to determining the consequences of climate change impacts on the ecosystem.

The paper outlines a work-in-progress to develop an archaeological approach to the historical reconstruction of sealing in the southern oceans. It indicates the topics such a work might include, and provides a brief example of how historical sources and archaeological evidence can be combined to understand better the experience of sealing in the 19 th century. Drawing on first-hand accounts of sealing and the evidence from 30 years of archaeological research in the region, it looks at the logistics of landing on sealing beaches, the building of shelters, food, cooking and eating equipment, clothing and pastimes.

Geologic studies indicate that prior to --40 Ma the Drake Passage was closed and the Central American Isthmus was open. The effect of these changes has been examined in an ocean general circulation model. Several sensitivity experiments were conducted, all with atmospheric forcing and other boundary conditions from the present climate, but with different combinations of closed and open gateways. In the first experiment, the only change involved closure of the Drake Passage. In agreement with earlier studies the barrier modified the geostrophic balance that now maintains the circumpolar flow in the southern ocean, with the net effect being decreased transport of the Antarctic Current and an approximate fourfold increase in outflow of Antarctic deep-bottom waters. The very large increase in Antarctic outflow suppresses North Atlantic Deep Water (NADW) formation. In addition to corroboration of results from earlier studies, our simulations provide several new insights into the role of a closed Drake Passage. A more geologically realistic closed Drake/open central American isthmus experiment produces essentially the same pattern of deepwater circulation from the first experiment, except that Antarctic outflow is about 20% less than the first experiment. The resultant unipolar deepwater circulation pattern for the second experiment is consistent with paleoceanographic observations from the early Cenozoic. A third Copyright 1993 by the American Geophysical Union. Paper number 93PA00893. 0883-8305/93/93PA-00893510.00 experiment involved an open Drake and open central American isthmus. In this experiment, Antarctic outflow is diminished to slightly above present levels but NADW production is still low due to free exchange of low-salinity surface water between the North Pacific and North Atlantic. The low level of thermohaline overturn should have reduced oceanic productivity in the Oligocene (.--30 Ma), a result in agreement with geologic observations. Finally, simulations with an energy balance model demonstrate that the changes in surface heat flux south of 60øS due to breaching of the Drake barrier do not result in temperature changes large enough to have triggered Antarctic glaciation. This last result suggests that some other factor (CO27) may be required for Antarctic ice sheet expansion in the Oligocene (-•30-34 Ma). Our results lend further support to the concept that even in the absence of changing boundary conditions due to ice sheet growth, variations in the geometry of the ocean basins can significantly influence ocean circulation patterns and the sediment record. The results also suggest that the primary polarities of the Cenozoic deepwater circulation may have been controlled by opening and closing of these two gateways. Cox, M.D., An idealized model of the world ocean, Part I, The global-scale water masses, J. Phys. Climate model comparison of Gondwanan and Laurentide glaciations, J. Geophys. Res., 96, 9217-9226, 1991.

Polar seaweeds are strongly adapted to the low temperatures of their environment, Antarctic species more strongly than Arctic species due to the longer cold water history of the Antarctic region. By reason of the strong isolation of the Southern Ocean the Antarctic marine flora is characterized by a high degree of endemism, whereas in the Arctic only few endemic species have been found so far. All polar species are strongly shade adapted and their phenology is finely tuned to the strong seasonal changes of the light conditions. The paper summarises the present knowledge of seaweeds from both polar regions with regard to the following topics: the history of seaweed research in polar regions; the environment of seaweeds in polar waters; biodiversity, biogeographical relationships and vertical distribution of Arctic and Antarctic seaweeds; life histories and physiological thallus anatomy; temperature demands and geographical distribution; light demands and depth zonation; the effect of salinity, temperature and desiccation on supraand eulittoral seaweeds; seasonality of reproduction and the physiological characteristics of C. Wiencke (&) AE U. H. Lü der microscopic developmental stages; seasonal growth and photosynthesis; elemental and nutritional contents and chemical and physical defences against herbivory. We present evidence to show that specific characteristics and adaptations in polar seaweeds help to explain their ecological success under environmentally extreme conditions. In conclusion, as a perspective and guide for future research we draw attention to many remaining gaps in knowledge.

ChEss (www.noc.soton.ac.uk/chess) is one of the 14 pilot projects within the Census of Marine Life initiative (www.coml.org). The aim of ChEss is to determine the biogeography of deep-water chemosynthetically-driven ecosystems and to understand the processes driving them. The main objectives are to assess and explain the global diversity, distribution and abundance of species from chemosynthetic systems including hydrothermal vents, cold seeps, whale falls, sunken wood and oxygen minimum zones where they intersect the deep seafloor along certain ocean margins. ChEss follows two approaches: 1-development of a web-based relational database for all species from deep-water chemosynthetic ecosystems including taxonomical, biological, ecological and distributional data as well as information on specific samples and collections (ChEssBase -www.noc.soton.ac.uk/chess/database/database.html); 2-development of a long-term international field programme for the exploration for and investigation of novel chemosynthetically-driven communities at key locations. Finally, ChEss is also developing a strong outreach and education component. One of the recently selected key target areas for ChEss investigations, and the subject of this meeting, are the Polar regions, both Arctic and Antarctic, in conjunction with the IPY. This region has been chosen to compliment the target regions (Atlantic Equatorial Belt, SE Pacific off Chile and New Zealand; see map on poster) in order to address specific scientific questions pertinent to biogeographic and biodiversity issues. Determining the evolutionary and ecological relationships amongst the fauna of polar chemosynthetic environments is crucial to understanding the processes that shape the distribution of species from chemosynthetic ecosystems at the global scale. Several polar chemosynthetic ecosystems (both hydrothermal vents and cold seeps) have been discovered to date and projects are underway to explore them using the latest technology, including Autonomous Underwater Vehicles and ROVs. The discovery of chemosynthetic ecosystems in the Polar regions is of particular importance as ridge systems that are geographically, hydrographically and/or topographically isolated (e.g., the Eastern Arctic field area) are more likely to have developed distinctive endemic biota and ecosystems. Hypotheses relating to hydrographic, bathymetric and biogeographic barriers may be tested by studying the relationships between these and other biogeographic regions.

A planktonic foraminiferal zonal scheme is presented for subdivision of the Upper Cretaceous pelagic carbonate sequence from southern mid-high latitudes. Definition of the zones is based on first and last occurrences of planktonic foraminifera from Ocean Drilling Program Holes 762C and 763B (Leg 122; Exmouth Plateau, south Indian Ocean). During the Late Cretaceous the studied holes were located close to 50 S and for the first time a complete sedimentary record for the mid-high latitudes was obtained. A detailed biostratigraphic analysis has allowed recognition of two new zones (Falsotruncana maslakovae Zone and Marginotruncana marianosi Zone) for the interval extending from the last occurrence of Helvetoglobotruncana helvetica to the first occurrence of Dicarinella asymetrica (upper Turonian-lower Santonian). From this study it is apparent that some low latitude (Globotruncana ventricosa, Hedbergella flandrini, Marginotruncana marianosi) and high latitude (Globigerinelloides impensus and Hedbergella sliteri) marker taxa display a vertical distribution at mid-high latitudes which is different from that known from low latitudes; moreover, one species (Heterohelix papula), overlooked at low latitudes, exhibits a restricted range that seems to be useful for chrono-biostratigraphic correlations: its appearance is suggested to coincide with the Coniacian/Santonian boundary. The proposed biozonation, which is integrated with calcareous nannofossil and magnetostratigraphic data available for the sections studied, is compared with both the low-latitude standard zonation and the planktonic foraminiferal zonal scheme for the circum-Antarctic region, in order to define a bio-chronostratigraphic scale that is useful for mid-high latitudes of the southern oceans.

The biomass size structure of pelagic communities provides a system level perspective that can be instructive when considering trophic interactions. Such perspectives can become even more powerful when combined with taxonomic information and stable isotope analysis. Here we apply these approaches to the pelagic community of the Scotia Sea (Southern Ocean) and consider the structure and development of trophic interactions over different years and seasons. Samples were collected from three open-ocean cruises during the austral spring 2006, summer 2008 and autumn 2009. Three main sampling techniques were employed: sampling bottles for microplankton (0-50 m), vertically hauled fine meshed nets for mesozooplankton (0-400 m) and coarse-meshed trawls for macrozooplankton and nekton (0-1000 m). All samples were identified to the lowest practicable taxonomic level and their abundance, individual body weight and biomass (in terms of carbon) estimated. Slopes of normalised biomass spectrum versus size showed a significant but not substantial difference between cruises and were between À 1.09 and À 1.06. These slopes were shallower than expected for a community at equilibrium and indicated that there was an accumulation of biomass in the larger size classes (10 1 -10 5 mg C ind À 1 ). A secondary structure of biomass domes was also apparent, with the domes being 2.5-3 log 10 intervals apart in spring and summer and 2 log 10 intervals apart in autumn. The recruitment of copepod-consuming macrozooplankton, Euphausia triacantha and Themisto gaudichaudii into an additional biomass dome was responsible for the decrease in the inter-dome interval in autumn. Predator to prey mass ratios estimated from stable isotope analysis reached a minimum in autumn while the estimated trophic level of myctophid fish was highest in that season. This reflected greater amounts of internal recycling and increased numbers of trophic levels in autumn compared to earlier times of the year. The accumulation of biomass in larger size classes throughout the year in the Scotia Sea may reflect the prevalence of species that store energy and have multiyear life-cycles.

Seagrasses, marine flowering plants, are widely distributed along temperate and tropical coastlines of the world. Seagrasses have key ecological roles in coastal ecosystems and can form extensive meadows supporting high biodiversity. The global species diversity of seagrasses is low (b60 species), but species can have ranges that extend for thousands of kilometers of coastline. Seagrass bioregions are defined here, based on species assemblages, species distributional ranges, and tropical and temperate influences. Six global bioregions are presented: four temperate and two tropical. The temperate bioregions include the Temperate North Atlantic, the Temperate North Pacific, the Mediterranean, and the Temperate Southern Oceans. The Temperate North Atlantic has low seagrass diversity, the major species being Zostera marina, typically occurring in estuaries and lagoons. The Temperate North Pacific has high seagrass diversity with Zostera spp. in estuaries and lagoons as well as Phyllospadix spp. in the surf zone. The Mediterranean region has clear water with vast meadows of moderate diversity of both temperate and tropical seagrasses, dominated by deep-growing Posidonia oceanica. The Temperate Southern Oceans bioregion includes the temperate southern coastlines of Australia, Africa and South America. Extensive meadows of low-to-high diversity temperate seagrasses are found in this bioregion, dominated by various species of Posidonia and Zostera. The tropical bioregions are the Tropical Atlantic and the Tropical Indo-Pacific, both supporting mega-herbivore grazers, including sea turtles and sirenia. The Tropical Atlantic bioregion has clear water with a high diversity of seagrasses on reefs and shallow banks, dominated by Thalassia testudinum. The vast Tropical Indo-Pacific has the highest seagrass diversity in the world, with as many as 14 species growing together on reef flats although seagrasses also occur in very deep waters. The global distribution of seagrass genera is remarkably consistent north and south of the equator; the northern and southern hemispheres share ten seagrass genera and only have one unique genus each. Some genera are much more speciose than others, with the genus Halophila having the most seagrass species. There are roughly the same number of temperate and tropical seagrass genera as well as species. The most widely distributed seagrass is Ruppia maritima, which occurs in tropical and temperate zones in a wide variety of habitats. Seagrass bioregions at the scale of ocean basins are identified based on species distributions which are supported by genetic patterns of diversity. Seagrass bioregions provide a useful framework for interpreting ecological, physiological and genetic results collected in specific locations or from particular species.

Sealing has been an industry in the North Atlantic and Arctic seas since at least 1593. Initially the profits from sealing were far less than those gained from whaling, and the sealing industry remained a minor, if locally important, activity for many communities. Sealing became better established as a global industry from the late 18th century onwards as it expanded into the South Atlantic and the Southern Ocean, and the paper focuses on the relationship between explorers' reports of new discoveries and the role of sealers in the official and unofficial charting of the islands of the southern oceans and in the independent search for new sealing grounds.

Pronounced changes in temperature, salinity (density) and upwelling have occurred in surface and deeper waters of the oceans, contributing with changing patterns and strength of winds to an alteration in ocean circulation. Together these changes have a potentially large impact through feedbacks on climate change.

Dinoflagellates are an important component of the extant eukaryotic plankton. Their organic-walled, hypnozygotic cysts (dinocysts) provide a rich, albeit incomplete, history of the group in ancient sediments. Building on pioneering studies of the late 1970s and 1980s, recent drilling in the Southern Ocean has provided a wealth of new dinocyst data spanning the entire Paleogene. Such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of Paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts.

Remote sensing of Southern Ocean chlorophyll concentrations is the most effective way to detect large-scale changes in phytoplankton biomass driven by seasonality and climate change. However, the current algorithms for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, algorithm OC4v6), the Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua, algorithm OC3M) and GlobColour significantly underestimate chlorophyll concentrations at high latitudes. Here we use a long-term dataset from the Southern Ocean  (20 - 160E) to develop more accurate algorithms for all three of these products in southern high latitude regions. These new algorithms improve in situ versus satellite chlorophyll coefficients of determination (r^2) from 0.27 to 0.46, 0.26 to 0.51 and 0.25 to 0.27, for OC4v6, OC3M and GlobColour, respectively, while addressing the underestimation problem. This study also revealed that pigment composition, which reflects species composition and physiology, is key to understanding the reasons for satellite chlorophyll underestimation in this region. These significantly improved algorithms will permit more accurate estimates of standing stocks and more sensitive detection of spatial and temporal changes in those stocks, with consequences for derived products such as primary production and carbon cycling.

Penguins are adapted to live in extreme environments, but they can be highly sensitive to climate change, which disrupts penguin life history strategies when it alters the weather, oceanography and critical habitats. For example, in the southwest Atlantic, the distributional range of the ice-obligate emperor and Adélie penguins has shifted poleward and contracted, while the ice-intolerant gentoo and chinstrap penguins have expanded their range southward. In the Southern Ocean, the El Niño-Southern Oscillation and the Southern Annular Mode are the main modes of climate variability that drive changes in the marine ecosystem, ultimately affecting penguins. The interaction between these modes is complex and changes over time, so that penguin responses to climate change are expected to vary accordingly, complicating our understanding of their future population processes. Penguins have long life spans, which slow microevolution, and which is unlikely to increase their tolerance to rapid warming. Therefore, in order that penguins may continue to exploit their transformed ecological niche and maintain their current distributional ranges, they must possess adequate phenotypic plasticity. However, past species-specific adaptations also constrain potential changes in phenology, and are unlikely to be adaptive for altered climatic conditions. Thus, the paleoecological record suggests that penguins are more likely to respond by dispersal rather than adaptation. Ecosystem changes are potentially most important at the borders of current geographic distributions, where penguins operate at the limits of their tolerance; species with low adaptability, particularly the ice-obligates, may therefore be more affected by their need to disperse in response to climate and may struggle to colonize new habitats. While future sea-ice contraction around Antarctica is likely to continue affecting the ice-obligate penguins, understanding the responses of the ice-intolerant penguins also depends on changes in climate mode periodicities and interactions, which to date remain difficult to reproduce in general circulation models.

Silicon isotopic signatures (delta30Si) of water column silicic acid (Si(OH)4) were measured in the Southern Ocean, along a meridional transect from South Africa (Subtropical Zone) down to 57° S (northern Weddell Gyre). This provides the first reported data of a summer transect across the whole Antarctic Circumpolar Current (ACC). delta30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional water transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determine different mixing interfaces: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the delta30Si alteration of the mixing products and with the exception of AASW, all mixing ...

Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro-and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae.

This study presents the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations related to desert dust aerosols, their direct radiative effect, and their impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional comparisons to Angström exponent (AE), coarse mode AOD and dust surface concentrations are included to extend the assessment of model performance and to identify common biases present in models. These data comprise a benchmark dataset that is proposed for model inspection and future dust model development. There are large differences among the global models that simulate the dust cycle and its impact on climate. In general, models simulate the climatology of vertically integrated parameters (AOD and AE) within a factor of two whereas the total deposition and surface concentration are reproduced within a factor of 10. In addition, smaller mean normalized bias and root mean square errors are obtained for the climatology of AOD and AE than for total deposition and surface concentration. Characteristics of the datasets used and their uncertainties may influence these differences. Large uncertainties still exist with respect to the deposition fluxes in the southern oceans. Further measurements and model studies are necessary to assess the general model performance to reproduce dust deposition in ocean regions sensible to iron contributions. Models overestimate the wet deposition in regions dominated by dry deposition. They generally simulate more realistic surface concentration at stations downwind of the main sources than at remote ones. Most models simulate the gradient in AOD and AE between the different dusty regions. However the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models simulate the offshore transport of West Africa throughout the year but they overestimate the AOD and they transport too fine particles. The models also reproduce the dust transport across the Atlantic in the summer in terms of both AOD and AE but not so well in winter-spring nor the southward displacement of the dust cloud that is responsible of the dust transport into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model bias with respect to AOD and AE to infer the bias of the dust emissions in Africa and the Middle East. According to this analysis we suggest that a range of possible emissions for North Africa is 400 to 2200 Tg yr-1 and in the Middle East 26 to 526 Tg yr-1.

During the Paleocene-Eocene Thermal Maximum (PETM), rapid release of isotopically light C to the ocean-atmosphere system elevated the greenhouse effect and warmed temperatures by 5-7°C for 10 5 yr. The response of the planktic ecosystems and productivity to the dramatic climate changes of the PETM may represent a significant feedback to the carbon cycle changes, but has been difficult to document. We examine Sr/Ca ratios in calcareous nannofossils in sediments spanning the PETM in three open ocean sites as a new approach to examine productivity and ecological shifts in calcifying plankton. The large heterogeneity in Sr/Ca among different nannofossil genera indicates that nannofossil Sr/Ca reflects primary productivity-driven geochemical signals and not diagenetic overprinting. Elevated Sr/Ca ratios in several genera and constant ratios in other genera suggest increased overall productivity in the Atlantic sector of the Southern Ocean during the PETM. Dominant nannofossil genera in tropical Atlantic and Pacific sites show Sr/Ca variations during the PETM which are comparable to background variability prior to the PETM. Despite acidification of the ocean there was not a productivity crisis among calcifying phytoplankton. We use the Pandora ocean box model to explore possible mechanisms for PETM productivity change. If independent proxy evidence for more stratified conditions in the Southern Ocean during the PETM is robust, then maintenance of stable or increased productivity there likely reflects increased nutrient inventories of the ocean. Increased nutrient inventories could have resulted from climatically enhanced weathering and would have important implications for burial rates of organic carbon and stabilization of climate and the carbon cycle.

Porifera (pore-bearers), commonly known as sponges, are sessile, colonial animals that are ubiquitous to most marine and freshwater environments. As an ecologically successful phyla, sponges having existed since the Precambrian (~580 Ma), and were major reef builders during the Palaeozoic and Mesozoic (542 to 65 Ma) (e.g. Krautter 1997, Li et al. 1998, Jackson et al.
2007). Even today, sponges are an abundant and highly diverse phylum, with approximately 8,500 valid species described so far (Van Soest et al. 2012a, b), but at least twice that number are predicted to be discovered in the near future (Hooper & Van Soest 2002; Van Soest et al., 2012a).

Patagonian toothfish (Dissostichus eleginoides) is a large notothenioid fish that supports valuable fisheries throughout the Southern Ocean. D. eleginoides are found on the southern shelves and slopes of South America and around the sub-Antarctic islands of the Southern Ocean. Patagonian toothfish are a long-lived species (> 50 years), which initially grow rapidly on the shallow shelf areas, before undertaking an ontogenetic migration into deeper water. Although they are active predators and scavengers, there is no evidence of large-scale geographic migrations, and studies using genetics, biochemistry, parasite fauna and tagging indicate a high degree of isolation between populations in the Indian Ocean, South Georgia and the Patagonian Shelf. Patagonian toothfish spawn in deep water (ca. 1000 m) during the austral winter, producing pelagic eggs and larvae. Larvae switch to a demersal habitat at around 100 mm (1-year-old) and inhabit relatively shallow water (< 300 m) until 6–7 years of age, when they begin a gradual migration into deeper water. As juveniles in shallow water, toothfish are primarily piscivorous, consuming the most abundant suitably sized local prey. With increasing size and habitat depth, the diet diversifies and includes more scavenging. Toothfish have weakly mineralised skeletons and a high fat content in muscle, which helps neutral buoyancy, but limits swimming capacity. Toothfish generally swim with labriform motion, but are capable of more rapid sub-carangiform swimming when startled. Toothfish were first caught as a by-catch (as juveniles) in shallow trawl fisheries, but following the development of deep water longlining, fisheries rapidly developed throughout the Southern Ocean. The initial rapid expansion of the fishery, which led to a peak of over 40,000 tonnes in reported landings in 1995, was accompanied by problems of bird by-catch and overexploitation as a consequence of illegal, unreported and unregulated fishing (IUU). These problems have now largely been addressed, but continued vigilance is required to ensure that the species is sustainably exploited and the ecosystem effects of the fisheries are minimised.